Cylinder Heads & Head Gaskets | OEM & Performance Spec

Cylinder Head or Head Gasket: Understanding What Needs Replacing

A cylinder head failure and a head gasket failure are not the same event, though they frequently occur together. Knowing which component has failed and whether both require replacement determines the correct scope of the repair before any parts are ordered. Misreading this distinction is what turns a head gasket job into a second strip-down.

When a Cylinder Head Replacement Is Required

A cylinder head must be replaced rather than resealed when the head itself is damaged beyond serviceable limits. The most common conditions that move a repair from gasket replacement to full head replacement include:

• A deck surface warped beyond the manufacturer's maximum flatness tolerance and cannot be surface-ground within the minimum allowable deck height specification
• Cracking between valve seats or across combustion chamber surfaces, particularly common in aluminium heads subjected to sustained overheating, where thermal cycling fractures the material.l
• Valve seat or guide damage that cannot be restored by standard insert replacement or guide sleeving
• Combustion chamber erosion in diesel cylinder heads caused by extended overheating or coolant contamination

In most overheating events, the head gasket fails first. The sustained heat that caused it, however, often warps or cracks the head simultaneously. Inspecting the head for flatness and integrity before reusing it with a new gasket is not a precaution; it is a required step.

When a Head Gasket Replacement Is Sufficient

If the cylinder head measures flat within specification and carries no visible cracks or chamber damage, a car head gasket replacement alone restores the seal. A blown head gasket fails most consistently at:

• The fire ring surrounding each combustion chamber, where clamping load and thermal cycling are most concentrated
• Coolant passages adjacent to combustion chambers, producing the coolant-in-oil contamination that is the most recognised signature of a failed cylinder head gasket
• Oil passages, less frequently, presenting as weeping at the head joint face rather than internal contamination.

Where the head is confirmed serviceable, and the block deck is flat and undamaged, the correct repair is a new cylinder head gasket to the correct thickness specification, torqued accurately on a clean and properly prepared mating surface.

OEM vs. Cometic Head Gaskets: Matching the Specification to the Application

Not every engine calls for the same head gasket specification. The two categories most relevant to CBT Auto Parts customers are OEM-quality gaskets for standard rebuilds and Cometic head gaskets for performance and modified applications. Choosing between them is not a preference; it is a technical decision based on the condition of the mating surfaces and the engine's intended output.

OEM-quality cylinder head gaskets restore the original compressed thickness, bore diameter, and fire ring specification. They maintain the factory compression ratio, meet the block and head surface finish requirements for composite construction, and are correct for any engine returning to standard output without machining.

Cometic head gaskets are multi-layer steel gaskets produced for performance and modified applications. Their key advantages over composite OEM gaskets include:

• Available in multiple compressed thickness options, enabling compression ratio correction when the head or block has been machined below original specification
• MLS construction requires a surface finish of 50 to 60 Ra on both mating faces, smoother than the finish acceptable for composite gaskets, and non-negotiable for a lasting seal
• Retain clamping load under elevated cylinder pressure far more effectively than composite alternatives, making them the correct specification for boosted or high-compression builds
• The appropriate choice for any engine where head resurfacing has reduced the original deck height and standard thickness is no longer achievable.

Fitting a Cometic head gasket on a surface that has not been prepared to MLS specification will result in a seal failure, regardless of how accurately the head bolts are torqued.

Platform Coverage: Cylinder Heads and Head Gaskets We Supply

CBT Auto Parts stocks cylinder heads and car engine head gaskets across the following commonly rebuilt platforms:

Diesel Platforms

• 6.5 turbo diesel cylinder head: replacement heads for the GM 6.5-litre turbodiesel covering standard and precombustion chamber configurations across truck and SUV applications
• CAT 3406 head gasket: cylinder head gaskets for the Caterpillar 3406, a high-hours diesel platform common across heavy trucks and construction equipment
• Cylinder head diesel: OEM-spec cylinder heads across a broad range of commercial and agricultural diesel engines

Petrol and Light Vehicle Platforms

Subaru head gasket OEM-spec and upgraded gasket specifications for the Subaru EJ engine family, which carries a well-documented failure history on specific variants across the EA and EJ series

• Vauxhall Corsa head gasket: replacement cylinder head gaskets across the most common Corsa engine codes
• Gasket cylinder head: OEM-spec head gaskets spanning a wide range of European and Japanese petrol applications

If your platform is not listed here, contact CBT Auto Parts with your engine code, current deck height measurement, and whether the head has been machined. Specifications are confirmed before any order is dispatched.

What to Source Alongside Cylinder Heads and Head Gaskets

A cylinder head removal exposes several components that should be assessed before reassembly. Addressing them during the same job avoids repeating the strip-down for parts that were at the end of their service life when the head came off.

Components to evaluate and source alongside any cylinder head or head gasket job include:

• Camshafts: In overhead cam engines, the camshaft is housed within or directly above the cylinder head. Head removal is the correct time to measure cam lobe height, inspect bearing journal condition, and replace the camshaft if it falls outside the manufacturer's service limit.
• Valve Train Parts: Valves, springs, guides, and stem seals are fully accessible once the head is removed. Worn valve train components can be replaced at this stage for the cost of parts alone. Leaving them in place adds the full cost of another strip-down to the next failure.
• Engine Gasket Kits: A complete engine gasket kit covers the full range of gaskets and seals disturbed during a cylinder head job: intake and exhaust manifold gaskets, cam cover gasket, and front cover seals among them. Sourcing a kit removes the risk of discovering a missing gasket mid-assembly.
• Engine Rebuild Kits: Where the head removal is part of a broader overhaul, a full rebuild kit consolidates all gaskets, seals, and related consumables into a single order so the job can be completed without interruption.

All of these sit within the Engine & Powertrain Parts range at CBT Auto Parts, so every component needed around a cylinder head job can be sourced and dispatched together.